We will measure the steady-state level of acetylenzyme intermediate of acetylcholinesterase in order to clarify the mechanism of substrate inhibition and the mechanism of a number of inhibitors. These measurements will indicate the relative effects on acylation and deacylation. For example, there is evidence that fluoride does not inhibit deacetylation, it definitely does not inhibit decarbamylation, yet the kinetics of fluoride inhibition are unusual and seem to require inhibition of deacylation. If deacylation is not inhibited the steady-state level of the acetyl-enzyme will decline from its normal value of 65 percent. In a similar way we will be able to tell whether substrate inhibition involves inhibition of acylation (one theory) or inhibition of deacylation (a second theory). Other kinetic observations will be clarified in a similar way.